cache

diff --git a/src/main/java/br/ufrgs/inf/prosoft/cache/Caffeine.java b/src/main/java/br/ufrgs/inf/prosoft/cache/Caffeine.java
index 7bfbb8f..ef65574 100644
--- a/src/main/java/br/ufrgs/inf/prosoft/cache/Caffeine.java
+++ b/src/main/java/br/ufrgs/inf/prosoft/cache/Caffeine.java
@@ -89,6 +89,7 @@ public class Caffeine<K, V> implements Cache<K, V> {
         V get = this.cache.getIfPresent(key);
         if (get == null) {
             registerEvent(EventType.MISS, key);
+            throw new KeyNotFoundException();
         }
         registerEvent(EventType.HIT, get);
         return get;

diff --git a/src/main/java/br/ufrgs/inf/prosoft/cache/CaffeineGetterCache.java b/src/main/java/br/ufrgs/inf/prosoft/cache/CaffeineGetterCache.java
index e036f6c..5d3f2c4 100644
--- a/src/main/java/br/ufrgs/inf/prosoft/cache/CaffeineGetterCache.java
+++ b/src/main/java/br/ufrgs/inf/prosoft/cache/CaffeineGetterCache.java
@@ -12,7 +12,7 @@ import java.util.function.Supplier;
  * @author root
  * @param <V>
  */
-public class CaffeineGetterCache<V> extends CaffeineSingleCache<Void, V> {
+public class CaffeineGetterCache<V> extends CaffeineSingleCache<String, V> {
 
     public CaffeineGetterCache(String name) {
         super(name);
@@ -31,27 +31,27 @@ public class CaffeineGetterCache<V> extends CaffeineSingleCache<Void, V> {
     }
 
     public void put(V value, long timeToLive) {
-        super.put(null, value, timeToLive);
+        super.put("", value, timeToLive);
     }
 
     public void put(V value) {
-        super.put(null, value);
+        super.put("", value);
     }
 
     public V get() throws KeyNotFoundException {
-        return super.get(null);
+        return super.get("");
     }
 
     public void invalidate() {
-        super.invalidate(null);
+        super.invalidate("");
     }
 
     public V computeIfAbsent(Supplier<V> supplier, long timeToLive) {
-        return super.computeIfAbsent(null, supplier, timeToLive);
+        return super.computeIfAbsent("", supplier, timeToLive);
     }
 
     public V computeIfAbsent(Supplier<V> supplier) {
-        return super.computeIfAbsent(null, supplier);
+        return super.computeIfAbsent("", supplier);
     }
 
 }